As the global death toll from the Covid-19 pandemic exceeds one million, the U.S. has passed its own milestone: 200,000 deaths caused by the new coronavirus. From the first known fatality in early February to the latest death count nearly eight months later, scientists and public-health authorities have been piecing together evidence about who the disease is killing and why.
Death-certificate data collected by the Centers for Disease Control and Prevention have shown some consistent trends—more deaths among men than women (54% versus 46% of the total), deaths skewing heavily toward the elderly, and minorities dying at disproportionate rates. Research has also shown people with underlying health problems, like obesity and cardiovascular trouble, are at higher risk.
The age data are stark: About 79% of recorded Covid-19 deaths are among people age 65 and over, while people under age 35 account for just 1% of known deaths from the disease. Nearly a third of Covid-19 deaths has hit people who are at least 85 years old, death-certificate data from about 188,000 deaths, the latest available, show.
This elderly population was affected substantially in the springtime, when significant outbreaks hammered northeastern states like New York, New Jersey and Massachusetts and spread through nursing homes. Deaths connected to long-term-care facilities recently topped 81,000 and have consistently made up about 40% of all U.S. Covid-19 deaths, according to a Wall Street Journal tally of state and federal data.
How deadly is Covid-19? How do scientists measure that?
To know how deadly Covid-19 is, scientists first need to know how many people became infected by the new coronavirus. Then they need a clear count of how many of those died of the virus. Both numbers are still difficult to pin down.
Spotty access to testing, and in some areas a lack of testing, have contributed to undercounting of infections, public-health researchers say. And many infected people never experience symptoms, making them less likely to ever seek a test. “We know we have missed so many infections,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
There are two widely referenced ways to estimate the Covid-19 death rate: based only on known cases, commonly called the case-fatality rate, or based on the larger estimate of how many people have likely had infections, called the infection-fatality rate.
Using the latter method, research suggests the virus kills about 0.6% of people it infects, but estimates vary widely and the rate varies significantly by age. This is far less than the death rate from other serious but less-widespread coronavirus infections—SARS and MERS, also known as Middle East respiratory syndrome—but about six times as deadly as the seasonal flu.
Antibody tests have helped this research by uncovering some prior infections, though the tests are known for issues including false positives. “It really just gives you a gestalt of what happened,” said David Brett-Major, an epidemiology professor at the University of Nebraska College of Public Health.
Researchers at Johns Hopkins University, which tracks case and death data in near real-time, estimate the U.S. case-fatality rate is 2.9%, based on recent counts of about 205,000 known deaths and 7,157,000 known cases the university has recorded on its widely referenced Covid-19 dashboard. But those numbers don’t take into account all the cases that haven’t been captured by testing.
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